David G. Elms

Achieving structural safety : theoretical considerations

Abstract The nature of safety and the related concepts of risk and hazard are defined and explored. Measures of safety are discussed, and its relation to sustainability. Threats to safety are categorised, after which the discussion moves to consideration of safety management. Emphasis is given to indirect means of ensuring safety, particularly codes of practice, quality assurance, three “enemies of knowledge”, and indicator methods.

Professional decisions: the central role of models

Engineering is largely concerned with models and modelling. Models provide a context in which decisions are made. Here, the modelling process is considered in a general sense and then the relationship with engineering models is developed. For understanding, a first step is to differentiate and categorise. Thus, 10 types of engineering models are proposed and their purposes with respect to professional decision-making are discussed. The role of models in engineering failures is also considered.

Professional decisions: responsibilities

The responsibilities which civil engineers, and particularly the engineer of record, accept are considered. The interaction with other decision-makers such as the owner, stakeholders, the law and contractors results in complexity that can be partially resolved by the introduction of protocols in the form of regulations and codes of practice. However, uncertainty always exists and can result in surprises that can produce both beneficial and bad results. The sections entitled the cast, protocols and reality, advocacy and surprise, and complexity cover these topics. The nature of responsibility is analysed. Professional engineers work within an increasingly complex environment and have a responsibility to acquire and use skills beyond those applicable to traditional technical issues.

A probabilistic model of fire spread with time effects

Abstract The paper outlines the principal elements of a probabilistic model that analyses the spread of fire in multi-compartment buildings with respect to time. The analysis uses a graph theoretic network and an event hierarchy to determine the probability of fire spreading to different locations. The probability of fire spreading between compartments is based on a comparison of the probability density functions of the expected fire resistance and the fire severity: failure being the condition that severity exceeds resistance. The model is designed as a comparative tool to compare the performance of different fire safety strategies by calculating a ‘cost index’ for each design, based on the probable extent of fire damage in the building. The analysis gives attention to the compatibility of fire resistance and fire severity, and their conversion in real time parameters.

Risk balancing in structural problems

A balanced-risk design is one in which the risks of failure in different modes are balanced against one another in such a way that the total risk is minimised, for a fixed overall safety expenditure. The problem is formulated in general terms. It is then simplified, and expressed in terms of readily-understood quantities so that the process is as transparent as possible. Its simplicity makes it usable on a spreadsheet. The technique is primarily applicable at the rough early design stage of a structural project. Examples of application are given in the areas of preliminary bridge and fire design and the importance of sensitivity studies is demonstrated.

Use of fuzzy sets in developing code risk factors

Abstract Fuzzy set theory is used to produce risk factor values for a building code. Working through reliability indices, a transformation is developed to convert estimates of relative social importance of a building into code load factors. The importance estimates are found by surveying knowledgeable members of society or playing their roles, and by using fuzzy set theory to combine their views according to their significance. An extension, again using fuzzy set theory, brings in the use of multiple criteria on which to base judgements. An example gives risk factors close to those in an existing code.

From a structure to a tree

Abstract A graph is decomposed into a series of overlapping clusters. The tightness of a cluster is measured by the trace of the third power of the interaction matrix of the graph. The clusters are linked to form a new graph, which is decomposed into a tree according to the closeness of the clusters: the concept of the closeness is analogus to the general gravitational law. The initial graph is not restricted to a series of binary relationships: both nodes and links may be assigned weights, and the links may be directed and asymmetric.

Intuitive decisions and heuristics – an alternative rationality

Two ways of making a decision are objectively using formal analysis and subjectively using intuition. Psychological research has shown that the latter leads to better decisions in complex situations. Intuitive decision-making uses simplified rules of thumb heuristics. In engineering terms, complexity implies complex systems. A set of rules and principles – heuristics – is presented as a guide for making subjective decisions in complex system contexts, one aspect of which is to provide quality control and guard against bias and error. An extended practical example of the use of these heuristics is given involving assessment of the safety of nuclear-powered ships.

Introducing ethics using structured controversies

This paper describes a method of introducing ethics to a second-year class of civil engineering students. The method, known as a ‘structured controversy’, takes the form of a workshop where the students assume the identity of stakeholders having an interest in a proposed development in an environmentally sensitive region. The instructor enhances the workshop by deliberately feeding incorrect information into a catalogue of facts that each stakeholder has at their disposal. After the workshop, the instructor draws out three ethical frameworks from which the stakeholders operate. A key component of the exercise is that the students do not know beforehand that the environmental workshop is being used to introduce ethics. When the connection is revealed, the students appreciate that much of their behaviour during the role-play was because they inadvertently adhered to an unknown ethical platform. Since it is an environmental simulation, an explicit connection can be made to the debate over ‘who’ to include in the moral community. In addition, a link can be drawn to the notion of sustainable development which, in this paper, is advocated as an ethical rather than a technical concept.

Engineering decisions: framework, process and concerns

Decisions are central to engineering processes and hold them together. It is argued that better decisions will lead to better engineering. To achieve better decisions requires that they be understood in detail. A typical decision is broken down into its essential requirements and processes, thus displaying the components of its framework. The process leads to the identification of a number of concerns. The components are discussed and a set of issues where more work needs to be done is identified. There are significant implications for both engineering practice and engineering education.